Atom

Smallest unit of an element retaining its chemical identity, with nucleus and electrons.

Short definition

Smallest unit of an element retaining its chemical identity, with nucleus and electrons.

Full explanation

Atom in the context of atomic structure: Smallest unit of an element retaining its chemical identity, with nucleus and electrons. In practice this means relating macroscopic observation (mass, pressure, color), particle-level picture (atoms, electrons, ions moving and rearranging), and symbolic representation (formulas, equations, units). For Atom, students connect the definition to linked lessons: do not just memorize the phrase — predict what changes when conditions change and check with dimensional analysis.

Notation and units

• Notation: X
• Common units: SI or derived, temperature in kelvins when in gas/energy contexts.
• Symbolic hint: See related formula if applicable.

Example

Example for atom: In a worked problem where this term appears, substitute measured values with correct units and check that the dimensional result matches the intended quantity. For instance, calculating a atom often uses the form $n=m/M$ or $c=n/V$ or $PV=nRT$ with $T$ in kelvins — illustrating how atom leads to a numerically different but dimensionally correct result when units are handled.

Confused with

• Molecule — distinction: Atom is smallest unit of an element retaining its chemical identity, with nucleus and electrons. while Molecule has a different defining property. See cross-link in glossary.

Related resources

• Topic: atomic-structure
• Formula library — when a specific equation involves this term it is linked.
• Constants — if a constant is required, it is sourced and versioned (NIST 2022).

Sources

• NIST Physical Constants 2022 (nist-2022, CODATA 2022). Accessed 2026-08-21.

Last reviewed: 2026-08-21 — Review due: 2027-08-21 — Author: Chemistry Fundamentals Editorial Team — Reviewer: Editorial Review Board (transparent placeholder).

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